Always be as specific and precise as possible. If you think that you can make your point more specific, then do so.
Avoid all statements like the following:

'Ever since the seventeenth century people have said X'.

'Since the Darwinian revolution it has been impossible to believe Y'.

'Since the Enlightenment everyone has agreed that the Bible must be discarded as a source of objective knowledge'.

Narrow such points down to refer to specific individuals and their specific arguments. Show your awareness of the subtle differences between the various approaches that have been taken to philosophical and theological questions in the past and the present. Whose theology or whose science are you referring to? Which representatives of which elements of which traditions do you have in mind?

Academic writers have two principal tasks: analysis and synthesis.

Analysis is the job of breaking down big questions and facts into smaller ones and providing specific, detailed, and exact descriptions and arguments. The end result of analysis is often to make the object of study seem very very complicated, multi-faceted, messy, and diffuse.

Synthesis is the job of re-building the many contingent, diffuse facts up into clear statements of general principles, guiding narratives, and universal trends.

Synthesis is a luxury to which you must earn the right. You have to show that you know about the messy contingent details in question before you can justifiably make synthetic declarations about general trends in the history of thought or make grand statements about science, philosophy, religion, culture etc. The way that you earn that right is by doing analysis; that is to say by learning specific, detailed facts and arguments. Synthetic statements not backed up by an analysis of the relevant facts and arguments are empty.

You need to strike a balance between showing your awareness of the big picture and showing that you are capable of fine-grained analysis. The introductory and concluding sections of your essay are normally the best places to show your awareness of the big picture – of the main issues and the main protagonists in the discussions or period you are writing about. In the rest of the essay, rather than trying to be exhaustive (which would be absolutely impossible even if it were desirable, which it is not), you should pick a few key points, whether they be particular historical events, or particular arguments, or particular individual thinkers, or particularly suggestive or problematic words in the essay title, and engage in a much closer analysis of them. So, in the body of your essay, you should be showing that you can think rigorously and analytically about quite specific ideas, rather than painting a big exhaustive picture of the topic in vague and general terms. Being aware of this need to keep the right balance between the big picture and detailed, close analysis is essential to writing good essays and to avoiding the tendency to write in a vague and sweeping way.